1. Field of the Invention
The present invention relates to a method and an apparatus for controlling a welding robot having an object supporter for supporting a welding object to be welded, and at least one welding torch capable of moving relatively to the welding object. More particularly, the present invention relates to a method and an apparatus for controlling a welding robot, which is capable of performing a real-time change of welding conditions while a plurality of welding conditions are applied in a single welding line.
2. Description of the Prior Art
A welding robot, particularly an arc welding robot, moves welding torches toward an object to be welded (hereinbelow, referred to `welding object`) fixed on a welding jig, and then welds the welding object while moving the welding object and/or the welding torch.
A control part is provided so that the welding operation is performed under predetermined welding conditions.
The control part determines the welding conditions applied to a welding portion on the basis of input parameters such as the type of the welding object, geometric data of the welding portion, the depth of penetration, a starting point of welding and a termination point of welding. The welding conditions include a welding current, a welding voltage, a distance between the welding torch and the welding object, a speed for supplying a wire, a relative velocity of the welding torch and the welding object.
In the conventional welding robot, predetermined welding conditions are applied without any alteration while a single welding line is welded. Generally, in a linear welding line, the welding environment such as the geometric contour of the welding portion, the depth of penetration and the temperature of the welding object, does not vary throughout the entire welding line. Therefore, the alteration of the welding conditions is scarcely needed during the welding operation for the linear welding line.
However, a case may inevitably occur that the welding conditions such as the welding current, the welding voltage, and the welding speed should be changed. For example, when a welding object rotating by a welding jig is welded along a circular path, the temperature of the welding object gradually rises because of a thermal conduction. In such a situation, if the welding operation is continued according to initial welding conditions, i. e., the welding conditions determined on the basis of the low temperature of the welding object, the welding object may be melt excessively, which may cause a defect of welding. Further, even in the linear welding line, the depth of penetration should be changed if the variations of the geometric contour of the welding portions or any other variations occur.
FIG. 8 is a schematic view for illustrating an example that the welding conditions are changed in the conventional welding robot. A welding torch 51 performs welding while moving along a welding line 53 extended from a welding starting point P0 to a welding termination point P2. The welding line 53 consists of a first welding segment 53a which should be welded under the first welding conditions, and a second welding segment 53b which should be welded under the second welding conditions. In the conventional welding robot, the first welding segment 53a is welded under the corresponding initial welding conditions, and the supply of electrical power is stopped in order to temporarily stop the welding operation when the welding torch 51 arrives at a condition change point P1 which lies between the first welding segment 53a and the second welding segment 53b. Then, the welding conditions are changed to the second welding conditions corresponding to the second welding segment 53b, and thereafter the welding operation is resumed in order to weld the second welding segment 53b.
Therefore, much time is consumed in stopping the welding operation and resetting the welding conditions, whereby welding efficiency is lowered. Further, at the condition change point P1, i. e., at the boundary between the first welding segment 53a and the second welding segment 53b, there occurs a discontinuity of welding, which may cause an abrupt alteration of the welding bead. In order to remove such a discontinuity, an after-treatment such as grinding or the like has to be performed by an operator, which is a troublesome task.